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Brightness Difference for Assessing “Dirt” on Adhesive Tape

  1. Turn on the Photovolt 577 reflectance meter equipped with the “W” search unit or a “Y” search unit with a green or blue filter and allow it to equilibrate for about 0.5 h. Depress the Blue or Green channel button.
  2. Place the black cavity standard on the search unit and zero the meter. Zero by pressing CHANGE and ZERO. Change to 0.0, or to .0 if necessary.
  3. Place the standard BRIGHTNESS plaque on a flat surface with the white side up.
  4. Place the search unit on the white plaque and key in the percentage printed on the back of the plaque for the appropriate color filter by pressing CHANGE and STD. Changing numbers is achieved by depressing the A, B and G buttons when in this position. At other times, the A, B, and G refer to amber, blue, and green when tristimulus values are being read. Press STD again to lock this number into the 577 memory.
  5. At the end of this exercise, place the samples on a flat surface backed by a stack of white paper. (To ensure that no light passes through the stack, place the stack on the search unit and observe – no light should be seen). If light is still seen, increase the stack of paper.  NOTE: It is easier to read the reflectance value of the samples if they are placed on the desk and the search unit is used in the inverted position. NOTE: It is your choice how you want to measure the tapes, but the standard plaque should be measured in the same manner as the samples. NOTE: The tapes sometimes are not the same for the entire length of the tape sample. This can be observed visually and the reflectance values will vary accordingly. Good analytical technique requires that you always measure in the same manner. Either decide to measure only one area of the tape (center, side, etc.) or take several readings on the entire length of the tape and average these.
  6. When finished with a series, subtract the “dirty” tape values from the “clean” tape values. The “clean” tape values will always be higher than the “dirty” tape values. The higher the %R, the “whiter” or “cleaner” the sample. This is superior to taking a reflectance reading only, for the clean tape may vary from one series to another, therefore, comparison of %R alone will not allow you to compare from one plant to another with any degree of accuracy.
EXAMPLE : Reflectance of “clean” tape 81.4%* Reflectance of “dirty” tape 70.6%* Difference 10.8% *”Clean” and “Dirty” tapes are the tapes on white backing which are submitted for analysis. It is understood that the backing material is essentially “white” and free of smudges, etc